New: Add overrides and files configuration options (refs #3611)

docs/user-guide/configuring.md

@@ -709,6 +709,61 @@ module.exports = {
 }
 ```
 
+## Configuration Based on Glob Patterns
+
+Sometimes a more fine-controlled configuration is necessary, for example if the configuration for files within the same directory has to be different. Therefore you can provide configurations under the `overrides` key that will only apply to files that match specific glob patterns, using the same format you would pass on the command line (e.g., `app/**/*.test.js`).
+
+### How it works
+
+* Glob pattern overrides can only be configured within `.eslintrc` files.
+* The patterns are applied against the file path relative to the directory of the `.eslintrc` file. For example, if your `.eslintrc` file has the path `/Users/john/workspace/any-project/.eslintrc` and the file you want to lint has the path `/Users/john/workspace/any-project/lib/util.js`, then the pattern provided in `.eslintrc` will be executed against the relative path `lib/util.js`.
+* Glob pattern overrides have higher precedence than the regular configuration in the same `.eslintrc` file.
+* A glob specific configuration works almost the same as the regular configuration in your `.eslintrc`, except that you can't define nested glob based configurations or use `extends`.
+* Multiple glob patterns can be provided within a single override block. The associated configuration will be applied to the intersection of the sets of files matched by each of the patterns. In other words, a file must match all the supplied patterns for the configuration to apply.
+
+### Relative glob patterns
+
+```
+project-root
+├── app
+│   ├── lib
+│   │   ├── foo.js
+│   │   ├── fooSpec.js
+│   ├── components
+│   │   ├── bar.js
+│   │   ├── barSpec.js
+│   ├── .eslintrc
+├── server
+│   ├── server.js
+│   ├── serverSpec.js
+├── .eslintrc
+```
+
+The config in `app/.eslintrc` defines the glob pattern `**/*Spec.js`. This pattern is relative to the base directory of `app/.eslintrc`. So, this pattern would match `app/lib/fooSpec.js` and `app/components/barSpec.js` but **NOT** `server/serverSpec.js`. If you defined the same pattern in the `.eslintrc` file within in the `project-root` folder, it would match all three of the `*Spec` files.
+
+### Example configuration
+
+In your `.eslintrc`:
+
+```json
+{
+  "rules": {
+    "quotes": [ 2, "double" ]
+  },
+
+  "overrides": [
+    {
+      "files": [ "lib/*.jsx" ],
+      "config": {
+        "rules": {
+          "quotes": [ 2, "single" ]
+        }
+      }
+    }
+  ]
+}
+```
+
 ## Comments in Configuration Files
 
 Both the JSON and YAML configuration file formats support comments (`package.json` files should not include them). You can use JavaScript-style comments or YAML-style comments in either type of file and ESLint will safely ignore them. This allows your configuration files to be more human-friendly. For example: